Method and device for correcting optical signals

ABSTRACT

An optical device is used to monitor an implant embedded in the tissue of a mammal (e.g., under the skin). The implant receives excitation light from the optical device and emits light that is detected by the optical device, including an analyte-dependent optical signal. Scatter and absorption properties of tissue change over time due to changes in hydration, blood perfusion and oxygenation. The optical device has an arrangement of light sources, filters and detectors to transmit excitation light within excitation wavelength ranges and to measure emitted light within detection wavelengths. Changes in scattering and absorption of light in the tissue, such as diffuse reflectance, are monitored. The light sources, filters and detectors may also be used to monitor autofluorescence in the tissue to correct autofluorescence background.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. provisional patent application 61/785,087 filed on Mar. 14, 2013, titled “Method and Device for Correcting Optical Signals”, which application is hereby incorporated by reference in its entirety.

BACKGROUND

The invention relates to a method and device for monitoring an implant, and in particular to a method and device for correcting luminescent signals emitted from the implant.

The monitoring of the level of analyte, such as glucose, lactate or oxygen, in certain individuals is important to their health. High or low levels of glucose, or other analytes, may have detrimental effects or be indicative of specific health states. The monitoring of glucose is particularly important to individuals with diabetes, a subset of whom must determine when insulin is needed to reduce glucose levels in their bodies or when additional glucose is needed to raise the level of glucose in their bodies.

A conventional technique used by many individuals with diabetes for personally monitoring their blood glucose level includes the periodic drawing of blood, the application of that blood to a test strip, and the determination of the blood glucose level using calorimetric, electrochemical, or photometric detection. This technique does not permit continuous or automatic monitoring of glucose levels in the body, but typically must be performed manually on a periodic basis. Unfortunately, the consistency with which the level of glucose is checked varies widely among individuals. Many people with diabetes find the periodic testing inconvenient, and they sometimes forget to test their glucose level or do not have time for a proper test. In addition, some individuals wish to avoid the pain associated with the test. Unmonitored glucose may result in hyperglycemic or hypoglycemic episodes. An implanted sensor that monitors the individual's analyte levels would enable individuals to monitor their glucose, or other analyte levels, more easily.

A variety of devices have been developed for monitoring of analytes (e.g., glucose) in the blood stream or interstitial fluid of various tissues. A number of these devices use sensors that are inserted into a blood vessel or under the skin of a patient. These implanted sensors are often difficult to read or to monitor optically, because of low levels of florescence in the presence of high scatter due to dynamic changes in skin conditions (e.g., blood level and hydration). The skin is highly scattering, and the scattering may dominate the optical propagation. Scatter is caused by index of refraction changes in the tissue, and the main components of scatter in the skin are due to lipids, collagen, and other biological components. The main absorption is caused by blood, melanin, water, and other components.

One device, disclosed in published US patent application 20090221891 to Yu, includes components of an assay for glucose. An optical signal is read out transcutaneously by external optics when the sensor is implanted in vivo. A fluorimeter separately measures, for a donor chromophore and an acceptor chromophore, an excitation light intensity, an ambient light intensity, and an intensity of combined luminescent and ambient light. Measurements are taken by holding the fluorimeter close to the skin and in alignment with the sensor. The final output provided is the normalized ratio between the luminescent intensity from the two fluorophores, which may be converted to analyte concentration using calibration data. A calibration curve is established empirically by measuring response versus glucose concentration. Although this device provides some light signal correction, it may still be difficult to obtain accurate readings due to dynamic skin changes that cause optical scattering and absorption of light emitted from the implant.

US patent application 20110028806 to Merritt discloses another procedure and system for measuring blood glucose levels. A set of photodiodes detects the luminescence and reflectance of light energy emitted from one or more emitters, such as LEDs, into a patient's skin. Small molecule metabolite reporters (SMMRs) that bind to glucose are introduced to tissue of the stratum corneum and the epidermis to provide more easily detected luminescence. The test results are calibrated with a reflectance intensity measurement taken at approximately the excitation wavelength. In addition, the method includes measuring a second luminescence and reflectance intensity to normalize data from the first set of measurements. First luminescence and reflectance intensity measurements are taken at a site treated with an SMMR. Second luminescence and reflectance intensity measurements are taken at an untreated, background site. The background measurement is then used to correct for the background tissue luminescence and absorption through a wavelength normalization. Although this method provides some light signal correction for background luminescence and reflectance, it may still be difficult to obtain accurate and/or consistent glucose readings from glucose-binding molecules in the epidermis.

There is still a need for a small, compact device that can accurately and consistently monitor an implanted sensor and provide signals to an analyzer without substantially restricting the movements and activities of a patient. Continuous and/or automatic monitoring of the analyte can provide a warning to the patient when the level of the analyte is at or near a threshold level. For example, if glucose is the analyte, then the monitoring device might be configured to warn the patient of current or impending hyperglycemia or hypoglycemia. The patient can then take appropriate actions.

SUMMARY

According to one aspect, a method is provided for correcting at least one analyte-dependent optical signal emitted from an implant. The implant is typically embedded in tissue of a mammalian body. The implant is capable of emitting, in response to excitation light within an excitation wavelength range, the analyte-dependent optical signal within an emission wavelength range. The method comprises transmitting first excitation light within the excitation wavelength range through the tissue to the implant and measuring a first optical signal emitted from the tissue, within the emission wavelength range, in response to the first excitation light. The method also comprises transmitting second excitation light within the emission wavelength range into the tissue and measuring a second optical signal emitted from the tissue, within the emission wavelength range, in response to the second excitation light. At least one corrected signal value is calculated in dependence upon the measured signals.

According to another aspect, an optical detection device is provided for monitoring an implant embedded in tissue of a mammalian body. The implant is capable of emitting, in response to excitation light within an excitation wavelength range, at least one analyte-dependent optical signal within an emission wavelength range. The device comprises a first light source arranged to transmit first excitation light within the excitation wavelength range through the tissue to the implant. A second light source is arranged to transmit second excitation light within the emission wavelength range into the tissue. At least one detector is arranged to measure, in response to the first excitation light, a first optical signal emitted from the tissue in the emission wavelength range and arranged to measure, in response to the second excitation light, a second optical signal emitted from the tissue in the emission wavelength range.

According to another aspect, a method is provided for correcting at least one analyte-dependent optical signal emitted from an implant embedded in tissue of a mammalian body. The implant is capable of emitting, in response to excitation light within an excitation wavelength range, the analyte-dependent optical signal within an emission wavelength range. The method comprises transmitting first excitation light within the excitation wavelength range through the tissue to the implant and measuring a first optical signal emitted from the tissue, within the emission wavelength range, in response to the first excitation light. The method also comprises transmitting second excitation light within the excitation wavelength range into the tissue and measuring a second optical signal emitted from the tissue, within the emission wavelength range, in response to the second excitation light. The second excitation light and the light emitted in response to the second excitation light form a light path that is spaced laterally from the implant a sufficient distance to avoid significant contribution from implant reporters (e.g., luminescent, luminescent, bioluminescent, or phosphorescent reporters). At least one corrected signal value is calculated in dependence upon the measured optical signals.

According to another aspect, an optical detection device is provided for monitoring an implant embedded in tissue of a mammalian body. The implant is capable of emitting, in response to excitation light within an excitation wavelength range, at least one analyte-dependent optical signal within an emission wavelength range. The device comprises a first light source arranged to transmit first excitation light in the excitation wavelength range through the tissue to the implant. A first detector is arranged to measure, in response to the first excitation light, a first optical signal emitted from the tissue in the emission wavelength range. A second light source is arranged to transmit second excitation light within the excitation wavelength range into the tissue. A second detector is arranged to measure, in response to the second excitation light, a second optical emitted from the tissue in the emission wavelength range. The second light source and the second detector are positioned with respect to each other such that the second excitation light and the light emitted in response to the second excitation light form a light path that is spaced laterally from the implant a sufficient distance to avoid significant contribution from implant reporters.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing aspects and advantages of the present invention will become better understood upon reading the following detailed description and upon reference to the drawings where:

FIG. 1 shows a schematic side view of an optical detection device for monitoring an implant according to one embodiment of the invention.

FIG. 2 shows a schematic side view of an optical detection device for monitoring an implant according to another embodiment of the invention.

FIG. 3 shows a schematic side view of aspects of an optical detection device according to another embodiment of the invention.

FIG. 4 shows a schematic plan view of an optical detection device according to another embodiment of the invention.

FIG. 5 shows a schematic cross-sectional view of the device of FIG. 4.

FIG. 6 shows a schematic side view of an optical detection device according to some embodiments of the invention.

FIG. 7 shows a schematic plan view of an optical detection device according to some embodiments of the invention.

FIG. 8 shows a schematic cross-sectional view of the device of FIG. 7.

FIG. 9 shows a schematic plan view of an optical detection device according to some embodiments of the invention.

FIG. 10 shows a schematic cross-sectional view of the device of FIG. 9.

FIG. 11 shows a schematic plan view of an optical detection device according to some embodiments of the invention.

FIG. 12 shows a schematic, exploded view of the device of FIG. 11.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

In the following description, it is understood that all recited connections between structures can be direct operative connections or indirect operative connections through intermediary structures. A set of elements includes one or more elements. Any recitation of an element is understood to refer to at least one element. A plurality of elements includes at least two elements. Unless otherwise required, any described method steps need not be necessarily performed in a particular illustrated order. A first element (e.g. data) derived from a second element encompasses a first element equal to the second element, as well as a first element generated by processing the second element and optionally other data. Making a determination or decision according to a parameter encompasses making the determination or decision according to the parameter and optionally according to other data. Unless otherwise specified, an indicator of some quantity/data may be the quantity/data itself, or an indicator different from the quantity/data itself. Computer programs described in some embodiments of the present invention may be stand-alone software entities or sub-entities (e.g., subroutines, code objects) of other computer programs. Computer readable media encompass non-transitory media such as magnetic, optic, and semiconductor storage media (e.g. hard drives, optical disks, flash memory, DRAM), as well as communications links such as conductive cables and fiber optic links According to some embodiments, the present invention provides, inter alia, computer systems comprising hardware (e.g. one or more processors and associated memory) programmed to perform the methods described herein, as well as computer-readable media encoding instructions to perform the methods described herein.

The following description illustrates embodiments of the invention by way of example and not necessarily by way of limitation.

FIG. 1 shows a schematic side view of an optical detection device 10 for monitoring an implanted sensor or implant 12, according to a first embodiment of the invention. The implant 12 is embedded in tissue of a mammalian body (which may be a portion of tissue that is attached or unattached to the rest of the body in various embodiments). The implant 12 is typically embedded under a surface of skin 14. The implant 12 is embedded at a first depth under the surface of the skin 14, which is preferably a sufficient depth to position the implant in the subcutaneous tissue (e.g., in the range of 1 to 5 mm under the surface of the skin 14). In some embodiments, the implant 12 is embedded in the tissue at a depth greater than or equal to 2 mm under the surface of the skin 14, and in other embodiments the implant 12 is embedded in the tissue at a depth greater than or equal to 4 mm under the surface of the skin.

The implant 12 is capable of emitting, in response to excitation light within an excitation wavelength range, at least one analyte-dependent optical signal within an emission wavelength range. The analyte may comprise, for example, glucose or other analytes in the body of the individual. Suitable optical signals include, but are not limited, to luminescent, luminescent, bioluminescent, phosphorescent, autoluminescence, and diffuse reflectance signals. In preferred embodiments, the implant 12 contains one or more luminescent dyes whose luminescence emission intensity varies in dependence upon the amount or presence of target analyte in the body of the individual.

A first light source 16 is arranged to transmit first excitation light within the excitation wavelength range from the surface of the skin 14 to the implant 12. A second light source 18 is arranged to transmit second excitation light from the surface of the skin 14 into the tissue 15. The second excitation light is preferably within the emission wavelength range of the analyte-dependent luminescent signal (e.g., the emission peak). Suitable light sources include, without limitation, lasers, semi-conductor lasers, light emitting diodes (LEDs), organic LEDs.

At least one detector, and more preferably at least two detectors 20, 22 are arranged with the light sources 16, 18. The first detector 20 is positioned to measure, in response to the first excitation light from the first light source 16, a first optical signal (e.g., the intensity of light) emitted at the surface of the skin 14 within the emission wavelength range. The detector 20 is also arranged to measure, in response to the second excitation light, a second optical signal emitted from the tissue 15 through the surface of the skin 14 within the emission wavelength range. Suitable detectors include, without limitation, photodiodes or CCDs. Although multiple detectors are preferred for some embodiments, one could use a single universal detector. The detectors 20, 22 are preferably filtered (e.g., dichroic filters or other suitable filters) to measure the optical signals emitted within respective wavelength ranges. In this example, a suitable luminescent dye sensitive to glucose concentration is Alexa 647 responsive to excitation light (absorption) in the range of about 600 to 650 nm (absorption peak 647 nm) and within an emission wavelength range of about 670 to 750 nm with an emission peak of about 680 nm.

In the operation of device 10, an analyte-dependent luminescent signal emitted from the implant 12 is corrected for diffuse reflectance and/or autofluorescence. The light source 16 is activated to transmit first excitation light within the excitation wavelength range from the surface of the skin 14 to the implant 12. The first detector 20 measures, in response to the first excitation light, a first optical signal emitted from the tissue 15 at the surface of the skin 14 within the emission wavelength range, as represented by a first light path 24 from the light source 16 to the implant 12 to the first detector 20. The light path 24 provides the primary analyte-dependent optical signal. The second light source 18 is activated to transmit second excitation light from the surface of the skin 14 to a second depth in the tissue 15 under the surface of the skin 14. The second excitation light is substantially within the emission wavelength range (e.g., the emission peak) of the analyte-dependent luminescent signal. The first detector 20 measures, in response to the second excitation light, a second optical signal emitted from the tissue 15 through the surface of the skin 14 within the emission wavelength range, as represented by a second light path 26.

The second optical signal may be used as a reference signal to correct the primary analyte-dependent optical signal for diffuse reflectance or scattering of light in the tissue 15. In some embodiments, the second depth to which the light path 26 extends below the surface of the skin 14 may be substantially equal to the first depth at which the implant 12 is embedded (e.g., in the subcutaneous tissue at a depth of 1 to 5 mm under the surface of the skin 14). In some embodiments, the light path 26 for the second optical signal extends to a depth greater than or equal to 2 mm under the surface of the skin 14, and in other embodiments the light path 26 for the second optical signal extends to a depth greater than or equal to 4 mm under the surface of the skin.

An additional correction factor may optionally be obtained by activating the first light source 16 to transmit third excitation light, within the excitation wavelength range, from the surface of the skin 14 to a third depth in the tissue 15. In some embodiments, the third depth may differ from the first and second depths, and the third depth may be in the range of 1 to 5 mm under the surface of the skin 14. The second detector 22 measures a third optical signal emitted from the tissue 15 through the surface of the skin 14 within the excitation wavelength range in response to the third excitation light, as represented by a third light path 28. At least one corrected signal value is calculated in dependence upon the measured optical signals. In one example, the primary analyte-dependent signal from the implant may be corrected as:

Corrected Signal=S(LS1,D1)*C(LS2,D1)*C(LS1,D2)  (1)

In equation (1) above, the term S(LS1, D1) represents the first optical signal, which is the primary analyte-dependent optical signal measured from the first light path 24 from the first light source 16 to the implant 12 to the first detector 20. The term C(LS2, D1) represents the second optical signal, which is a correction factor signal measured from the second light path 26 from the second light source 18 to the first detector 20. The term C(LS1, D2) represents an optional third optical signal, which is an additional correction factor signal measured from the third light path 28 from the first light source 16 to the second detector 22.

Thus, the primary analyte-dependent optical signal emitted from the implant 12 may be corrected for diffuse reflectance or scattering within the emission wavelength range of the analyte-dependent optical signal, to account for optical scattering or absorption of the signal in the tissue 15. The analyte-dependent optical signal may optionally be corrected for scattering, reflectance or attenuation in the excitation wavelength range to account for dynamic changes in skin properties. One advantage of correcting the analyte-dependent signal by one or more reference signals is that accurate and/or consistent glucose values may be determined from measurements of light emitted from an implant located relatively deep in the tissue, such as in the subcutaneous region. Light emitted from the implant 12 may be strongly modulated by the tissue 15 between the implant and the surface of the skin 14. Embodiments of the present invention provide means to correct for modulation of light emitted from the tissue 15, in addition to correction for excitation light and background or ambient light, if desired.

Another advantage is that measurements of the reference optical signals used for correction factors (such as diffuse reflectance, autofluorescence, and/or background light) are taken in the same region of tissue 15 in which the implant 12 is embedded in a few seconds of time or less, so that dynamic skin or tissue properties, that may vary within different regions of the body, are substantially the same for the correction signals as they are for the primary analyte-dependent signal at the time of measurement. Prior to executing optical reads for the analyte-dependent signal, the diffuse reflectance correction signal and/or the autofluorescence correction signal, a dark reading may be taken to account for background or ambient light, and this reading may be used to further correct the signals, e.g., by background subtraction. A preferred order of optical readings for the correction factors is background subtraction, autofluorescence correction, and diffuse reflectance correction, although no particular order is required.

In some embodiments, an analyte concentration (e.g., glucose level) is determined from the corrected signal value. Preferably a look-up table or calibration curve is used to determine the analyte concentration in dependence upon the corrected signal value. The look-up table or calibration curve may be in a microprocessor included with the optics. In some embodiments, the microprocessor is programmed to store measured signal values and/or to calculate corrected signal values. Alternatively, these functions may be performed in a separate processor or external computer in communication with the optical device. The external processor or computer receives data representative of the measured optical signals and calculates the corrected signal value and analyte concentration. Alternatively, multiple processors may be provided, e.g., providing one or more processors in the optical device that communicate (wirelessly or with wires) with one or more external processors or computers.

FIG. 2 shows another embodiment of an optical detection device 30 for monitoring an implant 12. In this embodiment, the implant 12 is further capable of emitting, in response to excitation light within a second excitation wavelength range (that may share or overlap the first emission wavelength range) at least one analyte-independent optical signal within a second emission wavelength range. The implant 12 preferably contains an analyte-independent luminescence dye that functions to control for non-analyte physical or chemical effects on a reporter dye (e.g., photo bleaching or pH). Multiple dyes may used. The analyte-independent optical signal is not modulated by analyte present in the tissue 15 and provides data for normalization, offset corrections, or internal calibration. The analyte-independent signal may compensate for non-analyte affects that are chemical or physiological (e.g., oxygen, pH, redox conditions) or optical (e.g., water, light absorbing/scattering compounds, hemoglobin). Alternatively, the analyte-independent signal may be provided by a stable reference dye in the implant 12. Suitable stable reference materials include, but are not limited to, lanthanide doped crystals, lanthanide doped nanoparticles, quantum dots, chelated lanthanide dyes, and metal (e.g., gold or silver) nanoparticles. The stable reference dye may provide a reference signal for other signals (e.g., to determine photo bleaching).

The second embodiment differs from the first embodiment described above in that the device 30 includes a third light source 40 for transmitting excitation light into the tissue 15 through the surface of the skin 14. In the operation of device 30, an analyte-dependent luminescent signal emitted from the implant 12 is corrected using three reference signals. The first light source 32 is activated to transmit excitation light within a first excitation wavelength range from the surface of the skin 14, through the tissue 15, to the implant 12. The first detector 34 measures, in response to the first excitation light, a first optical signal emitted from the tissue 15 at the surface of the skin 14 within a first emission wavelength range, as represented by a first light path 42 from the first light source 32, to the implant 12, and to the first detector 34. This first optical signal is the primary analyte-dependent optical signal.

The second light source 38 is activated to transmit second excitation light from the surface of the skin 14 to a second depth in the tissue 15. The second excitation light is preferably within the first emission wavelength range (e.g., the emission peak) of the primary analyte-dependent optical signal. The first detector 34 measures, in response to the second excitation light, a second optical signal emitted from the tissue 15 at the surface of the skin 14 within the emission wavelength range, as represented by a second light path 44. The second optical signal may be used to correct for diffuse reflectance or scattering of light in the tissue 15 between the implant 12 and the surface of the skin 14. In some embodiments, the depth of the second light path 44 may be substantially equal to the first depth at which the implant 12 is embedded (preferably in the subcutaneous tissue 1 to 5 mm under the surface of the skin 14). In some embodiments, the light path 44 for the second optical signal extends to a depth greater than or equal to 2 mm under the surface of the skin 14, and in other embodiments the light path 44 for the second optical signal extends to a depth greater than or equal to 4 mm under the surface of the skin.

Next, the light source 38 is activated to transmit third excitation light in the second excitation wavelength range from the surface of the skin 14 to the implant 12. The second detector 36 measures, in response to the third excitation light, a third optical signal emitted from the tissue 15 at the surface of the skin 14 within the second emission wavelength range, as represented by a third light path 46. In this embodiment, the third optical signal is the analyte-independent luminescent signal. Next, the third light source 40 is activated to transmit fourth excitation light from the surface of the skin 14 into the tissue 15. The fourth excitation light is preferably within the emission wavelength range of the analyte-independent luminescent signal. The detector 36 measures, in response to the fourth excitation light, a fourth optical signal emitted from the tissue 15 at the surface of the skin 14 within this emission wavelength range, as represented by a fourth light path 48. At least one corrected signal value is calculated in dependence upon the measured optical signals. In one example, the primary analyte-dependent signal from the implant 12 may be corrected as:

Corrected Signal=S(LS1,D1)*C(LS2,D1)/[S(LS2,D2)*C(LS3,D2)]  (2)

In equation (2) above, the term S(LS1, D1) represents the first optical signal which is the primary analyte-dependent signal measured from the first light path 42 from the first light source 32 to the implant 12 to the first detector 34. The term C(LS2, D1) represents the second optical signal, which is a correction factor signal measured from the second light path 44 from the second light source 38 to the first detector 34. The term S(LS2, D2) represents the third optical signal, which is the analyte-independent signal measured from the third light path 46 extending from the second light source 38 to the implant 12 to the second detector 36. The term C(LS3, D2) represents the fourth optical signal, which is a correction factor signal measured from the fourth light path 48 extending from the third light source 40 to the second detector 36.

In some embodiments in which two implant reporters (e.g., luminescent dyes) are utilized, it is possible that the implant reporters may share or overlap excitation (absorption) or emission wavelength ranges. For example, in the embodiment of FIG. 2, the emission wavelength range of the first dye, which provides the analyte-dependent luminescence signal, shares or overlaps the excitation wavelength range of the second dye, which provides the analyte-independent luminescence signal. In another embodiment, the first and second dyes may share or overlap excitation wavelength ranges (so that a common light source may be used) and emit optical signals within different emission wavelength ranges. In another embodiment, the first and second dyes may be excited by light within different excitation wavelength ranges and emit optical signals within the same or overlapping emission wavelength range(s).

FIG. 3 shows optical interrogation at different depths D2, D3, D4 in the tissue 15 relative to the first depth D1 of the implant 12 under the surface of the skin 14. The spacing distances S1, S2, S3 between the arrangement of detectors 52; 54, 56 and the light source 50 determines the depths D2, D3, D4 of the respective light paths. In some embodiments, readings for optical signal corrections are performed at multiple depths, as represented by the respective light paths, and the measured values of the reference optical signals used for correction are averaged for the correction factor. In some embodiments, the light path for the reference optical signal extends to a depth D2 in the tissue 15 that is greater than the depth D1 at which the implant 12 is embedded. The light path for the reference optical signal may also extend to a depth D3 in the tissue 15 such that the light path passes through the implant 12.

When the optical device has multiple possible combinations of spacing distances between the light sources and detectors as shown in FIGS. 3-9, implementation may be more flexible, because the depth of the implant 12 may be application-specific. In one embodiment, at least one analyte-independent signal, which may be emitted by the stable reference dye, is used to determine the appropriate depth for the light path(s) and resulting optical signal(s) measured to correct the analyte-dependent signal for diffuse reflectance and/or autofluorescence. Preferably a look-up table is used to determine, based on the measured intensity of the analyte-independent luminescent signal emitted from the implant, which of the possible depth(s) for normalization optical signals should be used, or more specifically which light source/detector pairing(s). The look-up table may be in a microprocessor included with the optical device, or in a separate processor or external computer in communication with the optical device that receives data representative of the measured optical signals (e.g., intensities of light measured within selected wavelengths).

In some embodiments, the processor is programmed to determine (e.g., by calculation or a look-up table) a quantity or weight assigned to measurements of one or more diffuse reflectance signals. The quantity or weight assigned to the measured diffuse reflectance signal may then be used in correcting or normalizing one or more implant reporter signals (e.g., the primary analyte-dependent signal emitted from the implant) to calculate the corrected signal value. The quantity or weight is preferably determined in dependence upon the intensity of an analyte-independent optical signal (e.g., from the stable reference dye). The intensity of the analyte-independent optical signal may vary with the depth of the implant in the tissue. For example, if the implant is embedded in tissue at a depth of 2 mm under the surface of the skin, the amount of light attenuation in the tissue will likely be less than if the implant were embedded at a depth of 4 mm. Reporter optical signals emitted from a shallower implant may require less of a correction factor for diffuse reflectance and/or autofluorescence than those signals emitted from an implant embedded at a greater depth. In some embodiments, the diffuse reflectance correction factor used to correct or normalize the analyte-dependent signal is proportional to depth, and the quantity or weight assigned to the diffuse reflectance measurement is determined in dependence upon the measurement of the analyte-independent signal.

FIG. 4 shows another embodiment of an optical device 60 having additional light sources and detectors with multiple possible combinations of spacing distances between the light sources and detectors. The light sources and detectors are arranged in a sensor patch 62 adapted to be placed on the surface of the skin, and described in greater detail below. At least one, and more preferably three central exciter light sources 64A, 64B, and 64C are positioned to transmit excitation light through a central via 66 in the patch 62. The central via 66 may contain one or more optical waveguide(s). At least one detector, and more preferably an inner ring of three central detectors 68A, 68B, and 68C are arranged around the central via 66. There is also preferably an outer ring 70 having multiple outer-ring exciter light sources and outer-ring detectors (in this example twenty-five outer-ring light sources and detectors) arranged in a substantially ring-shaped pattern, providing many permutations of possible optical channels. The combination of an excitation light source and a detection band is an optical channel. An example of one possible implementation of the optical device 60 will now be given with reference to FIGS. 4-11 and Table 1, describing twelve optical channels.

TABLE 1 Optical Emissions Channel Function Excitation Detected Exciter Detector Comments 1 Implant Excitation Peak Emission Peak Central Central Analyte-dependent 1 Reporter 1 Reporter 1 Reporter 1 Exciter 1 Detector 1 2 Implant Excitation Peak Emission Peak Central Central Analyte- Reporter 2 Reporter 2 Reporter 2 Exciter 2 Detector 2 independent 1 3 Implant Excitation Peak Emission Peak Central Central Stable Reference Reporter 3 Reporter 3 Reporter 3 Exciter 3 Detector 3 dye 4 Exciter Power Excitation Peak Excitation Peak Central Outer Power Normalization Reporter 1 Reporter 1 Exciter 1 Detector 6 Normalization 1 5 Exciter Power Excitation Peak Excitation Peak Central Outer Power Normalization Reporter 2 Reporter 2 Exciter 2 Detector 6 Normalization 2 6 Exciter Power Excitation Peak Excitation Peak Central Outer Power Normalization Reporter 3 Reporter 3 Exciter 3 Detector 6 Normalization 3 7 Diffuse Emission Peak Emission Peak Outer Outer Diffuse Reflectance Reflectance 1 Reporter 1 Reporter 1 Exciter 6 Detector 6 Data 8 Diffuse Emission Peak Emission Peak Outer Outer Diffuse Reflectance Reflectance 2 Reporter 2 Reporter 1 Exciter 7 Detector 6 Data 9 Diffuse Emission Peak Emission Peak Outer Outer Diffuse Reflectance Reflectance 3 Reporter 3 Reporter 1 Exciter 8 Detector 6 Data 10 Autofluorescence1 Excitation Peak Emission Peak Outer Outer Autofluorescence Reporter 1 Reporter 1 Exciter 1 Detector 1 and ambient light 11 Autofluorescence2 Excitation Peak Emission Peak Outer Outer Autofluorescence Reporter 2 Reporter 2 Exciter 2 Detector 2 and ambient light 12 Autofluorescence3 Excitation Peak Emission Peak Outer Outer Autofluorescence Reporter 3 Reporter 3 Exciter 3 Detector 3 and ambient light

As shown in Table 1, optical channels 1-3 function to measure three reporter dye signals from the implant, including an analyte-specific signal, an analyte-independent signal, and a stable reference dye signal. Optical channel 1 functions to measure an analyte-specific luminescent signal from the implant, such as a light signal whose intensity varies with glucose level. Other embodiments may include multiple analyte-dependent signals from the implant. Optical channel 2 functions to measure an analyte-independent control for non-analyte physical or chemical effects on the reporter dyes (e.g., photo bleaching, pH). Optical channel 3 functions to measure a stable reference dye (e.g., lanthanide).

As listed in Table 1 and shown in FIG. 4, each of the optical channels 1-3 comprises a respective pairing of one of the three central exciter light sources 64A, 64B, and 64C with a corresponding one of the three central detectors 68A, 68B, and 68C. FIG. 6 shows a schematic side view of the light paths for optical detection of the implant reporters. Excitation light is transmitted through the central via 66 (which preferably contains a monolithic waveguide) from the surface of the skin 14, through the tissue 15, and to the implant 12. Central detectors 68A, 68B, and 68C measure, in response to the excitation light, optical signals emitted from the tissue 15 at the surface of the skin 14 in respective emission wavelength ranges.

A suitable dye for the analyte-dependent signal is Alexa 647 which is responsive to excitation light within an excitation wavelength range of about 600 to 650 nm (excitation peak 647 nm) and within an emission wavelength range of about 670 to 750 nm with an emission peak of about 680 nm. A suitable dye for the analyte-independent signal is Alexa 750 which is responsive to excitation light within an excitation wavelength range of about 700 to 760 nm (excitation peak 750 nm) and within an emission wavelength range of about 770 to 850 nm with an emission peak of about 780 nm. A suitable stable reference dye is erbium with a first excitation light wavelength range of about 650 to 670 nm (excitation peak about 650 nm), a second excitation wavelength range of about 800 to 815 nm (with an excitation peak of about 805 nm), and an emission wavelength range of about 980 to 1050 nm (emission peak of about 1020 nm). In another embodiment, erbium an Alexa 647 may be excited from the same light source, which has the advantage that an optional step of power normalization between multiple light sources is reduced or eliminated.

Referring again to Table 1, optical channels 4-6 provide exciter power normalization signals, which are preferred in embodiments where more than one light source is used. The exciter power normalization signals are used to normalize differences in the power of excitation light output by each light source, which output power may vary slightly for each light source. As shown in FIGS. 4-5, the attenuation of excitation light traveling from central via 66 to outer ring 70 is measured, reducing or eliminating contribution by reporters (e.g., fluorophores) of the implant 12. The optical channels 4-6 comprise three combinations of pairings of the three central exciter light sources 64A, 64B, and 64C with outer-ring detector 6. Alternatively, multiple detectors may be used to detect the intensity of exciter power normalization signals, preferably outer-ring detectors. For exciter power normalization signals, excitation light within the excitation wavelength range of an implant reporter is transmitted into the tissue 15. An optical signal emitted from the tissue 15 within the excitation wavelength range is measured by the detector 6. The corrected signal value for an implant reporter may be normalized for exciter power of a respective light source, e.g., by dividing the optical signal measured for the reporter by the measured intensity of the excitation light within the excitation wavelength range.

Optical channels 7-9 (Table 1) provide diffuse reflectance measurements to correct the luminescent dye reporter signals from the implant. As shown in FIGS. 7-8, outer detector 6 measures attenuation by tissue 15 of light signals in the emission wavelength ranges of the luminescent reporter dyes of the implant 12. Optical channels 7-9 comprise three of the outer exciter light sources 71A, 71B, and 71C arranged in outside ring 70, each paired with the detector 6 in this example, and preferably positioned to provide a range of distances between each light source/detector combination, to compute diffuse reflectance correction values for each luminescent reporter dye of the implant 12. Rather than employing the detector 6 to measure all three optical signals, multiple detectors may be used in alternative embodiments.

Optical channels 10-12 (Table 1) provide measurements of autofluorescence and ambient light to correct the luminescent dye reporter signals from the implant. As shown in FIGS. 9-10, optical channels 10-12 comprise three pairs 73A, 73B, and 73C of the outer exciter light sources and outer-ring detectors arranged in the outside ring 70. The three pairs 73A, 73B, and 73C of the outer exciter light sources and outer detectors provide the same excitation and emission spectra of the three reporter luminescent dyes of the implant 12, and are located on outer ring 70 away from implant 12. In particular, each pair of outer exciter light source/detector for the autofluorescence measurement(s) are positioned with respect to each other such that the excitation light and the light emitted in response to the excitation light form a light path 78 that is spaced laterally from the implant 12 a sufficient distance to avoid significant contribution from implant fluorophores.

It is preferred that the lateral spacing S4 be greater than or equal to 0.25 cm, more preferably greater than 0.5 cm, and most preferably greater than 1 cm. It is also preferred that the depth of the light path 78 extend about 1 to 5 mm into the tissue 15 under the surface of the skin 14. When multiple pairs are used, each light path may have substantially the same depth or different depths, and the measured intensities of the autofluorescence optical signals may be averaged to obtain a correction factor. It is preferred that the contribution from the implant reporter(s) (e.g., fluorophores) to the autofluorescence measurement be less than 30% of the measured intensity, more preferably less than 20%, an most preferably less than 10%.

FIG. 11 shows a plan view of the sensor patch 62 having central via 66 for excitation light. Preferred dimensions of patch 62 may be, for example, a diameter of about 16 mm and a thickness T of about 1.6 mm. FIG. 12 shows a schematic, exploded view of the patch 62 comprising multiple layers in a stack. In some embodiments, the layers may comprise a plastic cover 80 having a preferred thickness of about 200 um, a light control film 82 having a preferred thickness of about 100 um, a filter 84 having a preferred thickness of about 200 um, another light control film 86 having a preferred thickness of about 100 um, a silicon layer 88 having a preferred thickness of about 200 um, a printed circuit board (PCB) 90 having a preferred thickness of about 400 um, a battery 92 having a preferred thickness of about 300 um, and a case 94 having a thickness of about 200 um. The PCB 90 may include a microprocessor that is programmed to store measured values and/or to calculate the corrected signal values as previously described. The light control film is a lens array with an aperture array on its back side.

It should be clear to one skilled in the art that embodiments of the described invention may include cabled or wireless hand-held readers, wireless skin patch readers, bench-top instruments, imaging systems, handheld devices (e.g., cell phones or mobile communication devices), smartphone attachments and applications, or any other configuration that utilizes the disclosed optics and algorithms.

Tissue optical heterogeneity in some cases may be significant. Thus, it may be advantageous to utilize a single light source and a single detector to assure that every color passes through the same optical pathway through the tissue. In one embodiment, a light source can be positioned with a set of moveable filters between the light source and the surface of the skin. Similarly a single photodetector can be utilized in place of separate discrete detector elements. The detector may be used to detect different colors by using moveable or changeable filters to enable multiple wavelengths to be measured. Changing or moving filters may be accomplished by a mechanical actuator controlling a rotating disc, filter strip or other means. Alternatively, optical filters may be coated with a material that when subjected to current, potential, temperature or another controllable influence, will change optical filtering properties, so that a single photodetector can serve to detect multiple colors.

It will be clear to one skilled in the art that the above embodiments may be altered in many ways without departing from the scope of the invention. For example, many different permutations or arrangements of one or more light sources, one or more detectors, filters, and/or fibers connecting the optical components may be used to realize the device and method of the invention. For example, in some embodiments the light sources and detectors are arranged with optical fibers or cables to transmit excitation light into the skin and measure optical signals emitted from the skin, without having to position the light sources and detectors directly on the skin of an individual. Presently preferred values for dimensions of the device and/or wavelength ranges may differ in alternative embodiments. Accordingly, the scope of the invention should be determined by the following claims and their legal equivalents. 

What is claimed is:
 1. A method for correcting at least one analyte-dependent optical signal emitted from an implant embedded in tissue of a mammalian body, the implant being capable of emitting, in response to excitation light within an excitation wavelength range, the analyte-dependent optical signal within an emission wavelength range, the method comprising: a) transmitting first excitation light within the excitation wavelength range through the tissue to the implant; b) measuring, in response to the first excitation light, a first optical signal emitted from the tissue within the emission wavelength range; c) transmitting second excitation light into the tissue, wherein the second excitation light is substantially within the emission wavelength range of the analyte-dependent optical signal; d) measuring, in response to the second excitation light, a second optical signal emitted from the tissue within the emission wavelength range; and e) calculating at least one corrected signal value in dependence upon the measured signals.
 2. The method of claim 1, wherein the second optical signal travels a light path that extends to a depth in the tissue that is substantially equal to the depth at which the implant is embedded.
 3. The method of claim 2, wherein the depths are in the range of 1 to 5 mm under a surface of skin.
 4. The method of claim 1, wherein the second optical signal travels a light path that extends to a depth in the tissue that is greater than the depth at which the implant is embedded.
 5. The method of claim 1, further comprising the steps of: transmitting third excitation light into the tissue, wherein the third excitation light is within the excitation wavelength range; and measuring, in response to the third excitation light, a third optical signal emitted from the tissue in the emission wavelength range, wherein the third optical signal travels a light path that is spaced laterally from the implant a sufficient distance to avoid significant contribution from implant reporters, and wherein the corrected signal value is calculated in further dependence upon the measured third optical signal.
 6. The method of claim 1, wherein the implant is embedded in subcutaneous tissue, and wherein the second optical signal travels a light path that extends to a depth in the tissue that is greater than or equal to 2 mm under a surface of skin.
 7. The method of claim 1, further comprising the steps of transmitting third excitation light into the tissue and measuring a third optical signal emitted from the tissue, wherein the implant is embedded at a first depth in the tissue, the second optical signal travels a light path that extends to a second depth in the tissue, the third optical signal travels another light path that extends to a third depth in the tissue, the third depth differs from the first and second depths, and the corrected signal value is calculated in further dependence upon the third optical signal.
 8. The method of claim 1, wherein the implant is embedded at a first depth in the tissue, the second optical signal travels a light path that extends to a second depth in the tissue, and the second depth is determined by transmitting excitation light within a second excitation wavelength range through the tissue to the implant, measuring at least one analyte-independent optical signal emitted from the tissue, and determining the second depth in dependence upon the analyte-independent optical signal.
 9. The method of claim 1, wherein the step of calculating at least one corrected signal value includes the steps of measuring at least one analyte-independent optical signal emitted from the implant and assigning a quantity or weight to the measurement of the second optical signal in dependence upon the measurement of the analyte-independent signal.
 10. The method of claim 1, further comprising the steps of: transmitting third excitation light within a second excitation wavelength range through the tissue to the implant; measuring, in response to the third excitation light, a third optical signal emitted from the tissue within a second emission wavelength range; transmitting fourth excitation light into the tissue, wherein the fourth excitation light is within the second emission wavelength range; and measuring, in response to the fourth excitation light, a fourth optical signal emitted from the tissue, wherein the corrected signal value is calculated in further dependence upon the measured third and fourth optical signals.
 11. The method of claim 1, further comprising the steps of transmitting third excitation light into the tissue and measuring a third optical signal emitted from the tissue, wherein the third excitation light is within the excitation wavelength range, and wherein the corrected signal value is calculated in further dependence upon the third optical signal.
 12. An optical detection device for monitoring an implant embedded in tissue of a mammalian body, the implant being capable of emitting, in response to excitation light within an excitation wavelength range, at least one analyte-dependent optical signal within an emission wavelength range, the device comprising: a) a first light source arranged to transmit first excitation light within the excitation wavelength range through the tissue to the implant; b) a second light source arranged to transmit second excitation light into the tissue, wherein the second excitation light is substantially within the emission wavelength range; and c) at least one detector arranged to measure, in response to the first excitation light, a first optical signal emitted from the tissue in the emission wavelength range and arranged to measure, in response to the second excitation light, a second optical signal emitted from the tissue in the emission wavelength range.
 13. The device of claim 12, further comprising at least one processor arranged to receive data to representative of the measured optical signals, wherein the processor is programmed to calculate at least one quantity or concentration of analyte according to the measured optical signals.
 14. The device of claim 12, wherein the second light source and at least one detector are arranged such that the second optical signal travels a light path that extends to a depth in the tissue that is substantially equal to the depth at which the implant is embedded.
 15. The device of claim 12, wherein the second light source and at least one detector are arranged such that the second optical signal travels a light path that extends to a depth in the tissue that is greater than the depth at which the implant is embedded.
 16. The device of claim 15, wherein the depths in the tissue are in a range of 1 to 5 mm under a surface of skin.
 17. The device of claim 12, further comprising: a third light source arranged to transmit third excitation light within the excitation wavelength range into the tissue; and at least a second detector arranged to measure, in response to the third excitation light, a third optical signal emitted from the tissue within the emission wavelength range, wherein the third light source and at least second detector are arranged such that the third excitation light and the light emitted in response to the third excitation light form a light path that is spaced laterally from the implant a sufficient distance to avoid significant contribution from implant reporters.
 18. The device of claim 12, wherein the implant is embedded in subcutaneous tissue, and the second light source and at least one detector are arranged such that the second optical signal travels a light path that extends to a depth in the tissue greater than or equal to 3 mm under a surface of skin.
 19. The device of claim 12, further comprising: a third light source arranged to transmit third excitation light into the tissue; and at least a second detector arranged to measure, in response to the third excitation light, a third optical signal emitted from the tissue, wherein the implant is embedded at a first depth in the tissue, the light sources and detectors are arranged such that the second optical signal travels a light path that extends to a second depth in the tissue, the third optical signal travels another light path that extends to a third depth in the tissue, and the third depth differs from the first and second depths.
 20. The device of claim 13, wherein the implant is embedded at a first depth in the tissue, the second light source and at least one detector are arranged such that the second optical signal travels a light path that extends to a second depth in the tissue, and the processor is further programmed to determine the second depth in dependence upon a measurement of at least one analyte-independent signal emitted from the implant.
 21. The device of claim 13, wherein the processor is further programmed to determine the corrected signal value by assigning a quantity or weight to the measurement of the second optical signal in dependence upon a measurement of at least one analyte-independent signal emitted from the implant.
 22. The device of claim 12, wherein the implant is further capable of emitting, in response to excitation light within a second excitation wavelength range, at least one analyte-independent optical signal within a second emission wavelength range, and the device further comprises: a third light source arranged to transmit third excitation light in the second excitation wavelength range through the tissue to the implant, wherein the at least one detector is arranged with the third light source to measure, in response to the third excitation light, a third optical signal emitted from the tissue in the second emission wavelength range; and to a fourth light source arranged to transmit fourth excitation light into the tissue, wherein the fourth excitation light is substantially within the second emission wavelength range, and wherein the at least one detector is arranged with the fourth light source to measure, in response to the fourth excitation light, a fourth optical signal emitted from the tissue.
 23. The device of claim 13, wherein the at least one detector is further arranged to measure, in response to third excitation light transmitted into the tissue, a third optical signal emitted from the tissue within the excitation wavelength range, and wherein the processor is further programmed to calculate the quantity or concentration of analyte in dependence upon the third optical signal.
 24. The device of claim 12, wherein the light sources and at least one detector are arranged in a sensor patch adapted to be placed on a surface of skin.
 25. A method for correcting at least one analyte-dependent optical signal emitted from an implant embedded in tissue of a mammalian body, the implant being capable of emitting, in response to excitation light within an excitation wavelength range, the analyte-dependent optical signal within an emission wavelength range, the method comprising: a) transmitting first excitation light within the excitation wavelength range through the tissue to the implant; b) measuring, in response to the first excitation light, a first optical signal emitted from the tissue within the emission wavelength range; c) transmitting second excitation light within the excitation wavelength range into the tissue; d) measuring, in response to the second excitation light, a second optical signal emitted from the tissue within the emission wavelength range, wherein the second excitation light and light emitted in response to the second excitation light form a light path that is spaced laterally from the implant a sufficient distance to avoid significant contribution from implant reporters; and e) determining at least one corrected signal value in dependence upon the measured optical signals.
 26. The method of claim 25, wherein the implant is embedded in subcutaneous tissue, and the light path extends to a depth in the tissue that is substantially equal to the depth at which the implant is embedded.
 27. The method of claim 25, wherein the implant is embedded at a first depth in the tissue, the light path extends to a second depth in the tissue, and the method further comprises the steps of transmitting third excitation light into the tissue and measuring a third optical signal emitted from the tissue, wherein the third optical signal travels another light path that extends to a third depth in the tissue that differs from the first and second depths, and wherein the corrected signal value is calculated in further dependence upon the third optical signal.
 28. The method of claim 25, further comprising the steps of: transmitting third excitation light within a second excitation wavelength range through the tissue to the implant; measuring, in response to the third excitation light, a third optical signal emitted from the tissue within a second emission wavelength range; transmitting fourth excitation light into the tissue, wherein the fourth excitation light is within the second emission wavelength range; and measuring, in response to the fourth excitation light, a fourth optical signal emitted from the tissue, wherein the corrected signal value is calculated in further dependence upon the measured third and fourth optical signals.
 29. The method of claim 25, wherein the lateral spacing of the light path from the implant is greater than or equal to 1 cm.
 30. The method of claim 25, further comprising the steps of: transmitting third excitation light into the tissue; and measuring, in response to the third excitation light, a third optical signal emitted from the tissue, wherein the third excitation light and the light emitted in response to the third excitation light form a second light path that is spaced laterally from the implant a sufficient distance to avoid significant contribution from implant reporters, and wherein the corrected signal value is calculated in further dependence upon the measured third optical signal.
 31. An optical detection device for monitoring an implant embedded in tissue of a mammalian body, the implant being capable of emitting, in response to excitation light within an excitation wavelength range, at least one analyte-dependent optical signal within an emission wavelength range, the device comprising: a) a first light source arranged to transmit first excitation light in the excitation wavelength range through the tissue to the implant; b) a first detector arranged to measure, in response to the first excitation light, a first optical signal emitted from the tissue in the emission wavelength range; c) a second light source arranged to transmit second excitation light in the excitation wavelength range into the tissue; and d) a second detector arranged to measure, in response to the second excitation light, a second optical signal emitted from the tissue within the emission wavelength range, wherein the second light source and the second detector are positioned with respect to each other such that the second excitation light and the light emitted in response to the second excitation light form a light path that is spaced laterally from the implant a sufficient distance to avoid significant contribution from implant reporters.
 32. The device of claim 31, further comprising at least one processor arranged to receive data representative of the measured optical signals and programmed to calculate at least one corrected signal value in dependence upon the measured optical signals.
 33. The device of claim 31, wherein the lateral spacing of the light path from the implant is greater than or equal to about 1 cm.
 34. The device of claim 31, wherein the light path extends to a depth in the tissue that is substantially equal to the depth at which the implant is embedded.
 35. The device of claim 31, wherein the implant is further capable of emitting, in response to excitation light having a second excitation wavelength range, at least one analyte-independent optical signal having a second emission wavelength range, and the device further comprises: a third light source arranged to transmit third excitation light in the second excitation wavelength range through the tissue to the implant; a third detector arranged to measure, in response to the third excitation light, a third optical signal emitted from the tissue in the second emission wavelength range; a fourth light source arranged to transmit fourth excitation light into the tissue, wherein the fourth excitation light is substantially within the second emission wavelength range; and a fourth detector arranged to measure, in response to the fourth excitation light, a fourth optical signal emitted from the tissue.
 36. The device of claim 31, further comprising: a third detector arranged to measure a third optical signal comprising light reflected from the tissue within the excitation wavelength range; and at least one processor arranged to receive data representative of the measured optical signals and programmed to calculate at least one corrected signal value in dependence upon the measured optical signals.
 37. The device of claim 31, further comprising: a third light source arranged to transmit third excitation light into the tissue; and a third detector arranged to measure, in response to the third excitation light, a third optical signal emitted from the tissue, wherein the third light source and the third detector are arranged with respect to each other such that the third excitation light and the light emitted in response to the third excitation light form a second light path that is spaced laterally from the implant a sufficient distance to avoid significant contribution from implant reporters.
 38. The device of claim 31, wherein the light sources and detectors are arranged in a sensor patch adapted to be placed on a surface of skin, the first light source being positioned to transmit the first excitation light through a central via in the patch, and the detectors being arranged in a pattern of one or more rings around the central via. 